It is known that the ability of an aircraft to develop sufficient lift to sustain flight is dependent upon the angle between the wing and the air through which the aircraft flies. This is known as the angle-of-attack of the aircraft. Since it is the prime purpose of an aircraft to stay in flight until the pilot desires to terminate that flight, it is essential that the pilot have knowledge of his angle-of-attack. Without an angle-of-attack display, the pilot must use air speed and then mentally correct it for changes in the aircraft weight, flap setting, power setting and load factor.
The use of wing surface pressures to obtain a pressure coefficient is old in the art; one such example is set forth in Spencer U.S. Pat. No. 2,986,033, which teaches the use of a pressure coefficient which is a function of impact pressure. Impact pressure is not readily determined accurately when the air craft is near stall. The Spencer Patent also uses the angle-of-attack for a display and refers to a ratio between the aircraft's present lift coefficient and the maximum lift coefficient (C.sub.L /C.sub.LMAX). However, as the flap setting is altered by the pilot, the angle-of-attack for the maximum coefficient of lift and for a coefficient of lift which equals zero will change. If the instrument is labeled in degrees, the pilot will only know the angle-of-attack and will not know at what angle stall will occur or the aircraft's relationship between the lift coefficients of zero and maximum. Therefore, it is highly desirable to provide an instrument for an aircraft which would indicate to the pilot his relative position with respect to stall at all times even when the flap setting and power or throttle setting are changed.
Accordingly, it is an object of this invention to provide in an instrumentation system a family of points on an aircraft at which pressure is detected which will provide a nondouble valued varying of a ratio between selected ones of the pressures detected even when the flap setting and power or throttle setting are changed and sufficient pressure to drive the transducers incorporated into the instrumentation system, which ratio will vary along a single continuous, not necessarily linear, line.
It is a further object of this invention to provide an instrumentation system, as aforesaid, wherein at least two points on the wing of the aircraft are provided which are spaced chordwise thereon at a specified span location from the aircraft fuselage, the remainder of the pressure locations being positioned for sensing the static or barometric pressure on the aircraft.
It is a further object of this invention to provide an instrumentation system, as aforesaid, which can be easily installed into existing aircraft with a minimum of alteration of the aircraft structure, thereby making it possible for such installations to be made in the field.
It is a further object of this invention to provide an instrumentation system, as aforesaid, which is reliable and durable and will indicate to the pilot of the aircraft the aircraft's position with respect to stall at all times even as the power or throttle setting and flap setting are changed.
It is a further object of this invention to provide in an instrumentation system on an aircraft, a family of points on the wing of the aircraft, each being located at a predetermined location on the wing so that the ratio of the differences between selected ones of the pressures will result in a nondouble valued varying coefficient of pressure ratio which remains nondouble valued even when the power or throttle setting and flap setting are altered and remains variable in magnitude along a single continuous, not necessarily linear, line.
It is a further object of this invention to provide an instrumentation system, as aforesaid, which produces an electrical signal output representing the aforesaid nondouble valued ratio totally in response to the particular placement of pressure sensing devices on the aircraft and totally independent of any equipment compensating for variations in the flap setting and/or power setting.